Intensity-modulated radiation therapy (IMRT), an advanced mode of high-precision radiotherapy, utilizes computer-controlled linear accelerators to deliver precise radiation doses to cancer cells. IMRT allows for the radiation dose to conform more precisely to the shape of the tumor by modulating, or controlling, the intensity of the radiation beam. IMRT also allows higher radiation doses to the cancer cells, while simultaneously blocking out the doses to normal organs and tissues, and thus reducing the risk of complications. Instead of maintaining a uniform radiation beam as used in conventional radiation therapy, IMRT uses blocks within the machine to divide the beam into multiple beams (beamlets), which have different intensities depending on the area being treated.

Treatment is carefully planned by using 3-D computed tomography (CT) images of the patient in conjunction with computerized dose calculations to determine the dose intensity pattern that will best conform to the tumor shape. Normally, several intensity-modulated fields coming from different directions are used to produce a custom radiation dose that maximizes tumor dose while also minimizing the dose to adjacent normal tissues. Since the ratio of normal tissue dose to tumor dose is greatly reduced using the IMRT method, higher and therefore more effective radiation doses are safely delivered to tumors, with fewer side effects, when compared to conventional radiotherapy. This also results in reduced treatment toxicity.

Radiation oncology facilities rely on a specially trained team for IMRT delivery. This team includes the radiation oncologist, medical radiation physicist, dosimetrist, and radiation therapists. The radiation oncologist, a specially trained physician, sets an individualized course of treatment for each patient, after a comprehensive series of tests and evaluations. The radiation physicist works in conjunction with the oncologist and is responsible for ensuring that the linear accelerator delivers the precise radiation dose and that computerized dose calculations are accurate. A dosimetrist, working under the supervision of the medical radiation physicist and radiation oncologist, calculates the IMRT exposures and beam configurations necessary to deliver the dose prescribed by the radiation oncologist. A team of highly trained radiation therapists are responsible for positioning the patients on the treatment table and operating the linear accelerator.

IMRT is used successfully in treatment of many forms of cancer, but has been specifically beneficial for patients diagnosed with prostate cancer. These patients benefit from a higher radiation dose to the cancer along with minimal dose exposure to the bladder and rectum. Additionally, researchers feel that by lowering the dose to pelvic nerves and blood vessels, IMRT may also produce less effect on sexual potency.